This invention relates to the construction of core assemblies for dynamoelectric machines. While the invention is described with particular reference to stator cores utilized in hermetic motor assemblies, those skilled in the art will recognize the wider applicability of the invention described hereinafter.
The prior art reveals a number of methods and machines for constructing core assemblies for electric motors in which the sole bonding medium is a adhesive. Previously known methods have included dipping cores which have been previously welded or cleated, dipping individual laminations or spraying them before they are stacked, forcing adhesive under pessure through a clamped core, or permitting the adhesive to wick inwardly of the lamination stack.
Among the problems experienced with cores having adhesive as the bonding medium is that relating to loss of bolt down torque in certain applications. It is conventional for motor manufacturers to provide stator core assemblies for hermetic compressors, for example, having bolt receiving openings through the core. The openings permit the compressor manufacturer to install the core assembly in a particular application. As may be surmised, mounting is accomplished by conventional threaded fasteners or bolts which are tightened against the core at some predetermined force, known in the field of this invention as bolt down torque. It has been found that when the laminations making up a core are coated with adhesive on their radial surfaces, baked, and thereafter mounted on a base by means of through bolts, the through bolts lose torque when the motor, sealed in a hermetic system, is subjected to the heat of a dehydration cycle to which a compressor is subjected in the course of manufacture. Cores so constructed also have been known to lose torque after field installation, permitting the core to shift. Shifting of the core results in compressor destruction if the core strikes the rotor assembly of the motor in the course of compressor operation. Solutions to loss of bolt down torque commonly have involved methods of constructing the core so that adhesive generally is not allowed to contact the area around the bolt holes, or removing the adhesive in later constructional steps if it is initially allowed along the bolt hole areas. While these prior art methods work well for their intended purposes, in general they are accomplished only by utilizing excessive amounts of adhesive material in conjunction with high tooling and high maintenance costs.
Adhesive bonded cores also have created heretofore unresolved peripheral manufacturing problems in that the adhesive, even where it was kept clear of the area surrounding the bolt holes, has been allowed to seep out along the inner edge of the lamination stack. Motor laminations conventionally have a central bore opening having a plurality of spaced teeth extending radially outwardly from the bore. Adjacent teeth define winding receiving slots. The slots are closed at one end and communicate with the bore at a second end along an opening between adjacent teeth. The inner edges of the teeth define both the bore opening and the inner edge of the lamination or lamination stack. In winding the core, it is conventional to insert the winding axially through the bore. The winding enters the slots along the openings between adjacent teeth. Machines for axially inserting the windings include tooling which rides along the inner edge of the lamination stack. The presence of adhesive along the inner edge of the lamination stack affects the useful life of the winding insertion tooling, resulting both in higher manufacturing costs because of increased maintenance and higher material costs.
The prior art does disclose apparatus which applies adhesive to a lamination stack at precise locations. For example, the U.S. patent to Zeis, U.S. Pat. No. 3,573,129, issued Mar. 30, 1971, shows a device and a method for applying adhesive to a stack of loose laminations at predetermined intervals along the outer edge of the lamination stack. While the Zeis patent works for its intended purpose, the degree of control available for controlling the amount of adhesive applied to a lamination stack has been unsatisfactory. That is to say, while the Zeis apparatus possesses sufficient adjustments for controlling the application of adhesive to a lamination stack at low manufacturing rates, in production use adhesive often appears along the inner edge of the lamination stack. Attempts to control with consistency the adhesive pattern of the Zeis apparatus at high manufacturing rates have been unsuccessful. As indicated, adhesive along the inner edge is an undesirable end result in the construction of an adhesive bonded core.
The method and apparatus disclosed hereinafter overcomes these previously unresolved prior art difficulties by utilizing a novel structural combination having a plurality of adjustments associated with it for controlling the application of adhesive to predetermined areas along the faces of adjacent laminations. The structure and method have resulted in the ability to provide an easy to monitor system for core production capable of high production rates and relatively close tolerance adhesive application so that the spreading of adhesive to the inner edge of the lamination stack is avoided, as is the application of adhesive about the lamination bolt hole area.
One of the objects of this invention is to provide a process for making core assemblies which accurately controls the application of adhesive to the core.
Another object of this invention is to produce an adhesive bonded core assembly having through bolt openings in it and an inner lamination edge in which both the inner lamination edge and the area about the through bolt openings are free of adhesive material.
Another object of this invention is to provide a low cost method for manufacturing adhesive bonded core assemblies.
Yet another object of this invention is to provide a device for applying adhesive to a stack of laminations having a plurality of easily adjustable adhesive application control means.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.